src/librustc/mir/visit.rs

   1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use hir::def_id::DefId;
  12 use ty::subst::Substs;
  13 use ty::{ClosureSubsts, GeneratorSubsts, Region, Ty};
  14 use mir::*;
  15 use syntax_pos::Span;
  16
  17 // # The MIR Visitor
  18 //
  19 // ## Overview
  20 //
  21 // There are two visitors, one for immutable and one for mutable references,
  22 // but both are generated by the following macro. The code is written according
  23 // to the following conventions:
  24 //
  25 // - introduce a `visit_foo` and a `super_foo` method for every MIR type
  26 // - `visit_foo`, by default, calls `super_foo`
  27 // - `super_foo`, by default, destructures the `foo` and calls `visit_foo`
  28 //
  29 // This allows you as a user to override `visit_foo` for types are
  30 // interested in, and invoke (within that method) call
  31 // `self.super_foo` to get the default behavior. Just as in an OO
  32 // language, you should never call `super` methods ordinarily except
  33 // in that circumstance.
  34 //
  35 // For the most part, we do not destructure things external to the
  36 // MIR, e.g. types, spans, etc, but simply visit them and stop. This
  37 // avoids duplication with other visitors like `TypeFoldable`.
  38 //
  39 // ## Updating
  40 //
  41 // The code is written in a very deliberate style intended to minimize
  42 // the chance of things being overlooked. You'll notice that we always
  43 // use pattern matching to reference fields and we ensure that all
  44 // matches are exhaustive.
  45 //
  46 // For example, the `super_basic_block_data` method begins like this:
  47 //
  48 // ```rust
  49 // fn super_basic_block_data(&mut self,
  50 //                           block: BasicBlock,
  51 //                           data: & $($mutability)* BasicBlockData<'tcx>) {
  52 //     let BasicBlockData {
  53 //         ref $($mutability)* statements,
  54 //         ref $($mutability)* terminator,
  55 //         is_cleanup: _
  56 //     } = *data;
  57 //
  58 //     for statement in statements {
  59 //         self.visit_statement(block, statement);
  60 //     }
  61 //
  62 //     ...
  63 // }
  64 // ```
  65 //
  66 // Here we used `let BasicBlockData { <fields> } = *data` deliberately,
  67 // rather than writing `data.statements` in the body. This is because if one
  68 // adds a new field to `BasicBlockData`, one will be forced to revise this code,
  69 // and hence one will (hopefully) invoke the correct visit methods (if any).
  70 //
  71 // For this to work, ALL MATCHES MUST BE EXHAUSTIVE IN FIELDS AND VARIANTS.
  72 // That means you never write `..` to skip over fields, nor do you write `_`
  73 // to skip over variants in a `match`.
  74 //
  75 // The only place that `_` is acceptable is to match a field (or
  76 // variant argument) that does not require visiting, as in
  77 // `is_cleanup` above.
  78
  79 macro_rules! make_mir_visitor {
  80     ($visitor_trait_name:ident, $($mutability:ident)*) => {
  81         pub trait $visitor_trait_name<'tcx> {
  82             // Override these, and call `self.super_xxx` to revert back to the
  83             // default behavior.
  84
  85             fn visit_mir(&mut self, mir: & $($mutability)* Mir<'tcx>) {
  86                 self.super_mir(mir);
  87             }
  88
  89             fn visit_basic_block_data(&mut self,
  90                                       block: BasicBlock,
  91                                       data: & $($mutability)* BasicBlockData<'tcx>) {
  92                 self.super_basic_block_data(block, data);
  93             }
  94
  95             fn visit_source_scope_data(&mut self,
  96                                            scope_data: & $($mutability)* SourceScopeData) {
  97                 self.super_source_scope_data(scope_data);
  98             }
  99
 100             fn visit_statement(&mut self,
 101                                block: BasicBlock,
 102                                statement: & $($mutability)* Statement<'tcx>,
 103                                location: Location) {
 104                 self.super_statement(block, statement, location);
 105             }
 106
 107             fn visit_assign(&mut self,
 108                             block: BasicBlock,
 109                             place: & $($mutability)* Place<'tcx>,
 110                             rvalue: & $($mutability)* Rvalue<'tcx>,
 111                             location: Location) {
 112                 self.super_assign(block, place, rvalue, location);
 113             }
 114
 115             fn visit_terminator(&mut self,
 116                                 block: BasicBlock,
 117                                 terminator: & $($mutability)* Terminator<'tcx>,
 118                                 location: Location) {
 119                 self.super_terminator(block, terminator, location);
 120             }
 121
 122             fn visit_terminator_kind(&mut self,
 123                                      block: BasicBlock,
 124                                      kind: & $($mutability)* TerminatorKind<'tcx>,
 125                                      location: Location) {
 126                 self.super_terminator_kind(block, kind, location);
 127             }
 128
 129             fn visit_assert_message(&mut self,
 130                                     msg: & $($mutability)* AssertMessage<'tcx>,
 131                                     location: Location) {
 132                 self.super_assert_message(msg, location);
 133             }
 134
 135             fn visit_rvalue(&mut self,
 136                             rvalue: & $($mutability)* Rvalue<'tcx>,
 137                             location: Location) {
 138                 self.super_rvalue(rvalue, location);
 139             }
 140
 141             fn visit_operand(&mut self,
 142                              operand: & $($mutability)* Operand<'tcx>,
 143                              location: Location) {
 144                 self.super_operand(operand, location);
 145             }
 146
 147             fn visit_ascribe_user_ty(&mut self,
 148                                      place: & $($mutability)* Place<'tcx>,
 149                                      variance: & $($mutability)* ty::Variance,
 150                                      user_ty: & $($mutability)* UserTypeProjection<'tcx>,
 151                                      location: Location) {
 152                 self.super_ascribe_user_ty(place, variance, user_ty, location);
 153             }
 154
 155             fn visit_retag(&mut self,
 156                            fn_entry: & $($mutability)* bool,
 157                            place: & $($mutability)* Place<'tcx>,
 158                            location: Location) {
 159                 self.super_retag(fn_entry, place, location);
 160             }
 161
 162             fn visit_place(&mut self,
 163                             place: & $($mutability)* Place<'tcx>,
 164                             context: PlaceContext<'tcx>,
 165                             location: Location) {
 166                 self.super_place(place, context, location);
 167             }
 168
 169             fn visit_static(&mut self,
 170                             static_: & $($mutability)* Static<'tcx>,
 171                             context: PlaceContext<'tcx>,
 172                             location: Location) {
 173                 self.super_static(static_, context, location);
 174             }
 175
 176             fn visit_projection(&mut self,
 177                                 place: & $($mutability)* PlaceProjection<'tcx>,
 178                                 context: PlaceContext<'tcx>,
 179                                 location: Location) {
 180                 self.super_projection(place, context, location);
 181             }
 182
 183             fn visit_projection_elem(&mut self,
 184                                      place: & $($mutability)* PlaceElem<'tcx>,
 185                                      location: Location) {
 186                 self.super_projection_elem(place, location);
 187             }
 188
 189             fn visit_branch(&mut self,
 190                             source: BasicBlock,
 191                             target: BasicBlock) {
 192                 self.super_branch(source, target);
 193             }
 194
 195             fn visit_constant(&mut self,
 196                               constant: & $($mutability)* Constant<'tcx>,
 197                               location: Location) {
 198                 self.super_constant(constant, location);
 199             }
 200
 201             fn visit_def_id(&mut self,
 202                             def_id: & $($mutability)* DefId,
 203                             _: Location) {
 204                 self.super_def_id(def_id);
 205             }
 206
 207             fn visit_span(&mut self,
 208                           span: & $($mutability)* Span) {
 209                 self.super_span(span);
 210             }
 211
 212             fn visit_source_info(&mut self,
 213                                  source_info: & $($mutability)* SourceInfo) {
 214                 self.super_source_info(source_info);
 215             }
 216
 217             fn visit_ty(&mut self,
 218                         ty: & $($mutability)* Ty<'tcx>,
 219                         _: TyContext) {
 220                 self.super_ty(ty);
 221             }
 222
 223             fn visit_user_type_projection(
 224                 &mut self,
 225                 ty: & $($mutability)* UserTypeProjection<'tcx>,
 226             ) {
 227                 self.super_user_type_projection(ty);
 228             }
 229
 230             fn visit_user_type_annotation(
 231                 &mut self,
 232                 ty: & $($mutability)* UserTypeAnnotation<'tcx>,
 233             ) {
 234                 self.super_user_type_annotation(ty);
 235             }
 236
 237             fn visit_region(&mut self,
 238                             region: & $($mutability)* ty::Region<'tcx>,
 239                             _: Location) {
 240                 self.super_region(region);
 241             }
 242
 243             fn visit_const(&mut self,
 244                            constant: & $($mutability)* &'tcx ty::Const<'tcx>,
 245                            _: Location) {
 246                 self.super_const(constant);
 247             }
 248
 249             fn visit_substs(&mut self,
 250                             substs: & $($mutability)* &'tcx Substs<'tcx>,
 251                             _: Location) {
 252                 self.super_substs(substs);
 253             }
 254
 255             fn visit_closure_substs(&mut self,
 256                                     substs: & $($mutability)* ClosureSubsts<'tcx>,
 257                                     _: Location) {
 258                 self.super_closure_substs(substs);
 259             }
 260
 261             fn visit_generator_substs(&mut self,
 262                                       substs: & $($mutability)* GeneratorSubsts<'tcx>,
 263                                     _: Location) {
 264                 self.super_generator_substs(substs);
 265             }
 266
 267             fn visit_local_decl(&mut self,
 268                                 local: Local,
 269                                 local_decl: & $($mutability)* LocalDecl<'tcx>) {
 270                 self.super_local_decl(local, local_decl);
 271             }
 272
 273             fn visit_local(&mut self,
 274                             _local: & $($mutability)* Local,
 275                             _context: PlaceContext<'tcx>,
 276                             _location: Location) {
 277             }
 278
 279             fn visit_source_scope(&mut self,
 280                                       scope: & $($mutability)* SourceScope) {
 281                 self.super_source_scope(scope);
 282             }
 283
 284             // The `super_xxx` methods comprise the default behavior and are
 285             // not meant to be overridden.
 286
 287             fn super_mir(&mut self,
 288                          mir: & $($mutability)* Mir<'tcx>) {
 289                 if let Some(yield_ty) = &$($mutability)* mir.yield_ty {
 290                     self.visit_ty(yield_ty, TyContext::YieldTy(SourceInfo {
 291                         span: mir.span,
 292                         scope: OUTERMOST_SOURCE_SCOPE,
 293                     }));
 294                 }
 295
 296                 // for best performance, we want to use an iterator rather
 297                 // than a for-loop, to avoid calling Mir::invalidate for
 298                 // each basic block.
 299                 macro_rules! basic_blocks {
 300                     (mut) => (mir.basic_blocks_mut().iter_enumerated_mut());
 301                     () => (mir.basic_blocks().iter_enumerated());
 302                 };
 303                 for (bb, data) in basic_blocks!($($mutability)*) {
 304                     self.visit_basic_block_data(bb, data);
 305                 }
 306
 307                 for scope in &$($mutability)* mir.source_scopes {
 308                     self.visit_source_scope_data(scope);
 309                 }
 310
 311                 self.visit_ty(&$($mutability)* mir.return_ty(), TyContext::ReturnTy(SourceInfo {
 312                     span: mir.span,
 313                     scope: OUTERMOST_SOURCE_SCOPE,
 314                 }));
 315
 316                 for local in mir.local_decls.indices() {
 317                     self.visit_local_decl(local, & $($mutability)* mir.local_decls[local]);
 318                 }
 319
 320                 self.visit_span(&$($mutability)* mir.span);
 321             }
 322
 323             fn super_basic_block_data(&mut self,
 324                                       block: BasicBlock,
 325                                       data: & $($mutability)* BasicBlockData<'tcx>) {
 326                 let BasicBlockData {
 327                     ref $($mutability)* statements,
 328                     ref $($mutability)* terminator,
 329                     is_cleanup: _
 330                 } = *data;
 331
 332                 let mut index = 0;
 333                 for statement in statements {
 334                     let location = Location { block: block, statement_index: index };
 335                     self.visit_statement(block, statement, location);
 336                     index += 1;
 337                 }
 338
 339                 if let Some(ref $($mutability)* terminator) = *terminator {
 340                     let location = Location { block: block, statement_index: index };
 341                     self.visit_terminator(block, terminator, location);
 342                 }
 343             }
 344
 345             fn super_source_scope_data(&mut self,
 346                                            scope_data: & $($mutability)* SourceScopeData) {
 347                 let SourceScopeData {
 348                     ref $($mutability)* span,
 349                     ref $($mutability)* parent_scope,
 350                 } = *scope_data;
 351
 352                 self.visit_span(span);
 353                 if let Some(ref $($mutability)* parent_scope) = *parent_scope {
 354                     self.visit_source_scope(parent_scope);
 355                 }
 356             }
 357
 358             fn super_statement(&mut self,
 359                                block: BasicBlock,
 360                                statement: & $($mutability)* Statement<'tcx>,
 361                                location: Location) {
 362                 let Statement {
 363                     ref $($mutability)* source_info,
 364                     ref $($mutability)* kind,
 365                 } = *statement;
 366
 367                 self.visit_source_info(source_info);
 368                 match *kind {
 369                     StatementKind::Assign(ref $($mutability)* place,
 370                                           ref $($mutability)* rvalue) => {
 371                         self.visit_assign(block, place, rvalue, location);
 372                     }
 373                     StatementKind::FakeRead(_, ref $($mutability)* place) => {
 374                         self.visit_place(
 375                             place,
 376                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 377                             location
 378                         );
 379                     }
 380                     StatementKind::SetDiscriminant{ ref $($mutability)* place, .. } => {
 381                         self.visit_place(
 382                             place,
 383                             PlaceContext::MutatingUse(MutatingUseContext::Store),
 384                             location
 385                         );
 386                     }
 387                     StatementKind::EscapeToRaw(ref $($mutability)* op) => {
 388                         self.visit_operand(op, location);
 389                     }
 390                     StatementKind::StorageLive(ref $($mutability)* local) => {
 391                         self.visit_local(
 392                             local,
 393                             PlaceContext::NonUse(NonUseContext::StorageLive),
 394                             location
 395                         );
 396                     }
 397                     StatementKind::StorageDead(ref $($mutability)* local) => {
 398                         self.visit_local(
 399                             local,
 400                             PlaceContext::NonUse(NonUseContext::StorageDead),
 401                             location
 402                         );
 403                     }
 404                     StatementKind::InlineAsm { ref $($mutability)* outputs,
 405                                                ref $($mutability)* inputs,
 406                                                asm: _ } => {
 407                         for output in & $($mutability)* outputs[..] {
 408                             self.visit_place(
 409                                 output,
 410                                 PlaceContext::MutatingUse(MutatingUseContext::AsmOutput),
 411                                 location
 412                             );
 413                         }
 414                         for (span, input) in & $($mutability)* inputs[..] {
 415                             self.visit_span(span);
 416                             self.visit_operand(input, location);
 417                         }
 418                     }
 419                     StatementKind::Retag { ref $($mutability)* fn_entry,
 420                                            ref $($mutability)* place } => {
 421                         self.visit_retag(fn_entry, place, location);
 422                     }
 423                     StatementKind::AscribeUserType(
 424                         ref $($mutability)* place,
 425                         ref $($mutability)* variance,
 426                         ref $($mutability)* user_ty,
 427                     ) => {
 428                         self.visit_ascribe_user_ty(place, variance, user_ty, location);
 429                     }
 430                     StatementKind::Nop => {}
 431                 }
 432             }
 433
 434             fn super_assign(&mut self,
 435                             _block: BasicBlock,
 436                             place: &$($mutability)* Place<'tcx>,
 437                             rvalue: &$($mutability)* Rvalue<'tcx>,
 438                             location: Location) {
 439                 self.visit_place(
 440                     place,
 441                     PlaceContext::MutatingUse(MutatingUseContext::Store),
 442                     location
 443                 );
 444                 self.visit_rvalue(rvalue, location);
 445             }
 446
 447             fn super_terminator(&mut self,
 448                                 block: BasicBlock,
 449                                 terminator: &$($mutability)* Terminator<'tcx>,
 450                                 location: Location) {
 451                 let Terminator {
 452                     ref $($mutability)* source_info,
 453                     ref $($mutability)* kind,
 454                 } = *terminator;
 455
 456                 self.visit_source_info(source_info);
 457                 self.visit_terminator_kind(block, kind, location);
 458             }
 459
 460             fn super_terminator_kind(&mut self,
 461                                      block: BasicBlock,
 462                                      kind: & $($mutability)* TerminatorKind<'tcx>,
 463                                      source_location: Location) {
 464                 match *kind {
 465                     TerminatorKind::Goto { target } => {
 466                         self.visit_branch(block, target);
 467                     }
 468
 469                     TerminatorKind::SwitchInt { ref $($mutability)* discr,
 470                                                 ref $($mutability)* switch_ty,
 471                                                 values: _,
 472                                                 ref targets } => {
 473                         self.visit_operand(discr, source_location);
 474                         self.visit_ty(switch_ty, TyContext::Location(source_location));
 475                         for &target in targets {
 476                             self.visit_branch(block, target);
 477                         }
 478                     }
 479
 480                     TerminatorKind::Resume |
 481                     TerminatorKind::Abort |
 482                     TerminatorKind::Return |
 483                     TerminatorKind::GeneratorDrop |
 484                     TerminatorKind::Unreachable => {
 485                     }
 486
 487                     TerminatorKind::Drop { ref $($mutability)* location,
 488                                            target,
 489                                            unwind } => {
 490                         self.visit_place(
 491                             location,
 492                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 493                             source_location
 494                         );
 495                         self.visit_branch(block, target);
 496                         unwind.map(|t| self.visit_branch(block, t));
 497                     }
 498
 499                     TerminatorKind::DropAndReplace { ref $($mutability)* location,
 500                                                      ref $($mutability)* value,
 501                                                      target,
 502                                                      unwind } => {
 503                         self.visit_place(
 504                             location,
 505                             PlaceContext::MutatingUse(MutatingUseContext::Drop),
 506                             source_location
 507                         );
 508                         self.visit_operand(value, source_location);
 509                         self.visit_branch(block, target);
 510                         unwind.map(|t| self.visit_branch(block, t));
 511                     }
 512
 513                     TerminatorKind::Call { ref $($mutability)* func,
 514                                            ref $($mutability)* args,
 515                                            ref $($mutability)* destination,
 516                                            cleanup,
 517                                            from_hir_call: _, } => {
 518                         self.visit_operand(func, source_location);
 519                         for arg in args {
 520                             self.visit_operand(arg, source_location);
 521                         }
 522                         if let Some((ref $($mutability)* destination, target)) = *destination {
 523                             self.visit_place(
 524                                 destination,
 525                                 PlaceContext::MutatingUse(MutatingUseContext::Call),
 526                                 source_location
 527                             );
 528                             self.visit_branch(block, target);
 529                         }
 530                         cleanup.map(|t| self.visit_branch(block, t));
 531                     }
 532
 533                     TerminatorKind::Assert { ref $($mutability)* cond,
 534                                              expected: _,
 535                                              ref $($mutability)* msg,
 536                                              target,
 537                                              cleanup } => {
 538                         self.visit_operand(cond, source_location);
 539                         self.visit_assert_message(msg, source_location);
 540                         self.visit_branch(block, target);
 541                         cleanup.map(|t| self.visit_branch(block, t));
 542                     }
 543
 544                     TerminatorKind::Yield { ref $($mutability)* value,
 545                                               resume,
 546                                               drop } => {
 547                         self.visit_operand(value, source_location);
 548                         self.visit_branch(block, resume);
 549                         drop.map(|t| self.visit_branch(block, t));
 550                     }
 551
 552                     TerminatorKind::FalseEdges { real_target, ref imaginary_targets} => {
 553                         self.visit_branch(block, real_target);
 554                         for target in imaginary_targets {
 555                             self.visit_branch(block, *target);
 556                         }
 557                     }
 558
 559                     TerminatorKind::FalseUnwind { real_target, unwind } => {
 560                         self.visit_branch(block, real_target);
 561                         if let Some(unwind) = unwind {
 562                             self.visit_branch(block, unwind);
 563                         }
 564                     }
 565                 }
 566             }
 567
 568             fn super_assert_message(&mut self,
 569                                     msg: & $($mutability)* AssertMessage<'tcx>,
 570                                     location: Location) {
 571                 use mir::interpret::EvalErrorKind::*;
 572                 if let BoundsCheck {
 573                         ref $($mutability)* len,
 574                         ref $($mutability)* index
 575                     } = *msg {
 576                     self.visit_operand(len, location);
 577                     self.visit_operand(index, location);
 578                 }
 579             }
 580
 581             fn super_rvalue(&mut self,
 582                             rvalue: & $($mutability)* Rvalue<'tcx>,
 583                             location: Location) {
 584                 match *rvalue {
 585                     Rvalue::Use(ref $($mutability)* operand) => {
 586                         self.visit_operand(operand, location);
 587                     }
 588
 589                     Rvalue::Repeat(ref $($mutability)* value, _) => {
 590                         self.visit_operand(value, location);
 591                     }
 592
 593                     Rvalue::Ref(ref $($mutability)* r, bk, ref $($mutability)* path) => {
 594                         self.visit_region(r, location);
 595                         let ctx = match bk {
 596                             BorrowKind::Shared => PlaceContext::NonMutatingUse(
 597                                 NonMutatingUseContext::SharedBorrow(*r)
 598                             ),
 599                             BorrowKind::Shallow => PlaceContext::NonMutatingUse(
 600                                 NonMutatingUseContext::ShallowBorrow(*r)
 601                             ),
 602                             BorrowKind::Unique => PlaceContext::NonMutatingUse(
 603                                 NonMutatingUseContext::UniqueBorrow(*r)
 604                             ),
 605                             BorrowKind::Mut { .. } =>
 606                                 PlaceContext::MutatingUse(MutatingUseContext::Borrow(*r)),
 607                         };
 608                         self.visit_place(path, ctx, location);
 609                     }
 610
 611                     Rvalue::Len(ref $($mutability)* path) => {
 612                         self.visit_place(
 613                             path,
 614                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 615                             location
 616                         );
 617                     }
 618
 619                     Rvalue::Cast(_cast_kind,
 620                                  ref $($mutability)* operand,
 621                                  ref $($mutability)* ty) => {
 622                         self.visit_operand(operand, location);
 623                         self.visit_ty(ty, TyContext::Location(location));
 624                     }
 625
 626                     Rvalue::BinaryOp(_bin_op,
 627                                      ref $($mutability)* lhs,
 628                                      ref $($mutability)* rhs) |
 629                     Rvalue::CheckedBinaryOp(_bin_op,
 630                                      ref $($mutability)* lhs,
 631                                      ref $($mutability)* rhs) => {
 632                         self.visit_operand(lhs, location);
 633                         self.visit_operand(rhs, location);
 634                     }
 635
 636                     Rvalue::UnaryOp(_un_op, ref $($mutability)* op) => {
 637                         self.visit_operand(op, location);
 638                     }
 639
 640                     Rvalue::Discriminant(ref $($mutability)* place) => {
 641                         self.visit_place(
 642                             place,
 643                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Inspect),
 644                             location
 645                         );
 646                     }
 647
 648                     Rvalue::NullaryOp(_op, ref $($mutability)* ty) => {
 649                         self.visit_ty(ty, TyContext::Location(location));
 650                     }
 651
 652                     Rvalue::Aggregate(ref $($mutability)* kind,
 653                                       ref $($mutability)* operands) => {
 654                         let kind = &$($mutability)* **kind;
 655                         match *kind {
 656                             AggregateKind::Array(ref $($mutability)* ty) => {
 657                                 self.visit_ty(ty, TyContext::Location(location));
 658                             }
 659                             AggregateKind::Tuple => {
 660                             }
 661                             AggregateKind::Adt(_adt_def,
 662                                                _variant_index,
 663                                                ref $($mutability)* substs,
 664                                                _user_substs,
 665                                                _active_field_index) => {
 666                                 self.visit_substs(substs, location);
 667                             }
 668                             AggregateKind::Closure(ref $($mutability)* def_id,
 669                                                    ref $($mutability)* closure_substs) => {
 670                                 self.visit_def_id(def_id, location);
 671                                 self.visit_closure_substs(closure_substs, location);
 672                             }
 673                             AggregateKind::Generator(ref $($mutability)* def_id,
 674                                                      ref $($mutability)* generator_substs,
 675                                                      _movability) => {
 676                                 self.visit_def_id(def_id, location);
 677                                 self.visit_generator_substs(generator_substs, location);
 678                             }
 679                         }
 680
 681                         for operand in operands {
 682                             self.visit_operand(operand, location);
 683                         }
 684                     }
 685                 }
 686             }
 687
 688             fn super_operand(&mut self,
 689                              operand: & $($mutability)* Operand<'tcx>,
 690                              location: Location) {
 691                 match *operand {
 692                     Operand::Copy(ref $($mutability)* place) => {
 693                         self.visit_place(
 694                             place,
 695                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 696                             location
 697                         );
 698                     }
 699                     Operand::Move(ref $($mutability)* place) => {
 700                         self.visit_place(
 701                             place,
 702                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move),
 703                             location
 704                         );
 705                     }
 706                     Operand::Constant(ref $($mutability)* constant) => {
 707                         self.visit_constant(constant, location);
 708                     }
 709                 }
 710             }
 711
 712             fn super_ascribe_user_ty(&mut self,
 713                                      place: & $($mutability)* Place<'tcx>,
 714                                      _variance: & $($mutability)* ty::Variance,
 715                                      user_ty: & $($mutability)* UserTypeProjection<'tcx>,
 716                                      location: Location) {
 717                 self.visit_place(
 718                     place,
 719                     PlaceContext::NonUse(NonUseContext::AscribeUserTy),
 720                     location
 721                 );
 722                 self.visit_user_type_projection(user_ty);
 723             }
 724
 725             fn super_retag(&mut self,
 726                            _fn_entry: & $($mutability)* bool,
 727                            place: & $($mutability)* Place<'tcx>,
 728                            location: Location) {
 729                 self.visit_place(
 730                     place,
 731                     PlaceContext::MutatingUse(MutatingUseContext::Retag),
 732                     location,
 733                 );
 734             }
 735
 736             fn super_place(&mut self,
 737                             place: & $($mutability)* Place<'tcx>,
 738                             context: PlaceContext<'tcx>,
 739                             location: Location) {
 740                 match *place {
 741                     Place::Local(ref $($mutability)* local) => {
 742                         self.visit_local(local, context, location);
 743                     }
 744                     Place::Static(ref $($mutability)* static_) => {
 745                         self.visit_static(static_, context, location);
 746                     }
 747                     Place::Promoted(ref $($mutability)* promoted) => {
 748                         self.visit_ty(& $($mutability)* promoted.1, TyContext::Location(location));
 749                     },
 750                     Place::Projection(ref $($mutability)* proj) => {
 751                         self.visit_projection(proj, context, location);
 752                     }
 753                 }
 754             }
 755
 756             fn super_static(&mut self,
 757                             static_: & $($mutability)* Static<'tcx>,
 758                             _context: PlaceContext<'tcx>,
 759                             location: Location) {
 760                 let Static {
 761                     ref $($mutability)* def_id,
 762                     ref $($mutability)* ty,
 763                 } = *static_;
 764                 self.visit_def_id(def_id, location);
 765                 self.visit_ty(ty, TyContext::Location(location));
 766             }
 767
 768             fn super_projection(&mut self,
 769                                 proj: & $($mutability)* PlaceProjection<'tcx>,
 770                                 context: PlaceContext<'tcx>,
 771                                 location: Location) {
 772                 let Projection {
 773                     ref $($mutability)* base,
 774                     ref $($mutability)* elem,
 775                 } = *proj;
 776                 let context = if context.is_mutating_use() {
 777                     PlaceContext::MutatingUse(MutatingUseContext::Projection)
 778                 } else {
 779                     PlaceContext::NonMutatingUse(NonMutatingUseContext::Projection)
 780                 };
 781                 self.visit_place(base, context, location);
 782                 self.visit_projection_elem(elem, location);
 783             }
 784
 785             fn super_projection_elem(&mut self,
 786                                      proj: & $($mutability)* PlaceElem<'tcx>,
 787                                      location: Location) {
 788                 match *proj {
 789                     ProjectionElem::Deref => {
 790                     }
 791                     ProjectionElem::Subslice { from: _, to: _ } => {
 792                     }
 793                     ProjectionElem::Field(_field, ref $($mutability)* ty) => {
 794                         self.visit_ty(ty, TyContext::Location(location));
 795                     }
 796                     ProjectionElem::Index(ref $($mutability)* local) => {
 797                         self.visit_local(
 798                             local,
 799                             PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy),
 800                             location
 801                         );
 802                     }
 803                     ProjectionElem::ConstantIndex { offset: _,
 804                                                     min_length: _,
 805                                                     from_end: _ } => {
 806                     }
 807                     ProjectionElem::Downcast(_adt_def, _variant_index) => {
 808                     }
 809                 }
 810             }
 811
 812             fn super_local_decl(&mut self,
 813                                 local: Local,
 814                                 local_decl: & $($mutability)* LocalDecl<'tcx>) {
 815                 let LocalDecl {
 816                     mutability: _,
 817                     ref $($mutability)* ty,
 818                     ref $($mutability)* user_ty,
 819                     name: _,
 820                     ref $($mutability)* source_info,
 821                     ref $($mutability)* visibility_scope,
 822                     internal: _,
 823                     is_user_variable: _,
 824                     is_block_tail: _,
 825                 } = *local_decl;
 826
 827                 self.visit_ty(ty, TyContext::LocalDecl {
 828                     local,
 829                     source_info: *source_info,
 830                 });
 831                 for (user_ty, _) in & $($mutability)* user_ty.contents {
 832                     self.visit_user_type_projection(user_ty);
 833                 }
 834                 self.visit_source_info(source_info);
 835                 self.visit_source_scope(visibility_scope);
 836             }
 837
 838             fn super_source_scope(&mut self,
 839                                       _scope: & $($mutability)* SourceScope) {
 840             }
 841
 842             fn super_branch(&mut self,
 843                             _source: BasicBlock,
 844                             _target: BasicBlock) {
 845             }
 846
 847             fn super_constant(&mut self,
 848                               constant: & $($mutability)* Constant<'tcx>,
 849                               location: Location) {
 850                 let Constant {
 851                     ref $($mutability)* span,
 852                     ref $($mutability)* ty,
 853                     ref $($mutability)* user_ty,
 854                     ref $($mutability)* literal,
 855                 } = *constant;
 856
 857                 self.visit_span(span);
 858                 self.visit_ty(ty, TyContext::Location(location));
 859                 drop(user_ty); // no visit method for this
 860                 self.visit_const(literal, location);
 861             }
 862
 863             fn super_def_id(&mut self, _def_id: & $($mutability)* DefId) {
 864             }
 865
 866             fn super_span(&mut self, _span: & $($mutability)* Span) {
 867             }
 868
 869             fn super_source_info(&mut self, source_info: & $($mutability)* SourceInfo) {
 870                 let SourceInfo {
 871                     ref $($mutability)* span,
 872                     ref $($mutability)* scope,
 873                 } = *source_info;
 874
 875                 self.visit_span(span);
 876                 self.visit_source_scope(scope);
 877             }
 878
 879             fn super_user_type_projection(
 880                 &mut self,
 881                 ty: & $($mutability)* UserTypeProjection<'tcx>,
 882             ) {
 883                 let UserTypeProjection {
 884                     ref $($mutability)* base,
 885                     projs: _, // Note: Does not visit projection elems!
 886                 } = *ty;
 887                 self.visit_user_type_annotation(base);
 888             }
 889
 890             fn super_user_type_annotation(
 891                 &mut self,
 892                 _ty: & $($mutability)* UserTypeAnnotation<'tcx>,
 893             ) {
 894             }
 895
 896             fn super_ty(&mut self, _ty: & $($mutability)* Ty<'tcx>) {
 897             }
 898
 899             fn super_region(&mut self, _region: & $($mutability)* ty::Region<'tcx>) {
 900             }
 901
 902             fn super_const(&mut self, _const: & $($mutability)* &'tcx ty::Const<'tcx>) {
 903             }
 904
 905             fn super_substs(&mut self, _substs: & $($mutability)* &'tcx Substs<'tcx>) {
 906             }
 907
 908             fn super_generator_substs(&mut self,
 909                                       _substs: & $($mutability)* GeneratorSubsts<'tcx>) {
 910             }
 911
 912             fn super_closure_substs(&mut self,
 913                                     _substs: & $($mutability)* ClosureSubsts<'tcx>) {
 914             }
 915
 916             // Convenience methods
 917
 918             fn visit_location(&mut self, mir: & $($mutability)* Mir<'tcx>, location: Location) {
 919                 let basic_block = & $($mutability)* mir[location.block];
 920                 if basic_block.statements.len() == location.statement_index {
 921                     if let Some(ref $($mutability)* terminator) = basic_block.terminator {
 922                         self.visit_terminator(location.block, terminator, location)
 923                     }
 924                 } else {
 925                     let statement = & $($mutability)*
 926                         basic_block.statements[location.statement_index];
 927                     self.visit_statement(location.block, statement, location)
 928                 }
 929             }
 930         }
 931     }
 932 }
 933
 934 make_mir_visitor!(Visitor,);
 935 make_mir_visitor!(MutVisitor,mut);
 936
 937 pub trait MirVisitable<'tcx> {
 938     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>);
 939 }
 940
 941 impl<'tcx> MirVisitable<'tcx> for Statement<'tcx> {
 942     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>)
 943     {
 944         visitor.visit_statement(location.block, self, location)
 945     }
 946 }
 947
 948 impl<'tcx> MirVisitable<'tcx> for Terminator<'tcx> {
 949     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>)
 950     {
 951         visitor.visit_terminator(location.block, self, location)
 952     }
 953 }
 954
 955 impl<'tcx> MirVisitable<'tcx> for Option<Terminator<'tcx>> {
 956     fn apply(&self, location: Location, visitor: &mut dyn Visitor<'tcx>)
 957     {
 958         visitor.visit_terminator(location.block, self.as_ref().unwrap(), location)
 959     }
 960 }
 961
 962 /// Extra information passed to `visit_ty` and friends to give context
 963 /// about where the type etc appears.
 964 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 965 pub enum TyContext {
 966     LocalDecl {
 967         /// The index of the local variable we are visiting.
 968         local: Local,
 969
 970         /// The source location where this local variable was declared.
 971         source_info: SourceInfo,
 972     },
 973
 974     /// The return type of the function.
 975     ReturnTy(SourceInfo),
 976
 977     YieldTy(SourceInfo),
 978
 979     /// A type found at some location.
 980     Location(Location),
 981 }
 982
 983 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 984 pub enum NonMutatingUseContext<'tcx> {
 985     /// Being inspected in some way, like loading a len.
 986     Inspect,
 987     /// Consumed as part of an operand.
 988     Copy,
 989     /// Consumed as part of an operand.
 990     Move,
 991     /// Shared borrow.
 992     SharedBorrow(Region<'tcx>),
 993     /// Shallow borrow.
 994     ShallowBorrow(Region<'tcx>),
 995     /// Unique borrow.
 996     UniqueBorrow(Region<'tcx>),
 997     /// Used as base for another place, e.g. `x` in `x.y`. Will not mutate the place.
 998     /// For example, the projection `x.y` is not marked as a mutation in these cases:
 999     ///
1000     ///     z = x.y;
1001     ///     f(&x.y);
1002     ///
1003     Projection,
1004 }
1005
1006 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1007 pub enum MutatingUseContext<'tcx> {
1008     /// Appears as LHS of an assignment.
1009     Store,
1010     /// Can often be treated as a `Store`, but needs to be separate because
1011     /// ASM is allowed to read outputs as well, so a `Store`-`AsmOutput` sequence
1012     /// cannot be simplified the way a `Store`-`Store` can be.
1013     AsmOutput,
1014     /// Destination of a call.
1015     Call,
1016     /// Being dropped.
1017     Drop,
1018     /// Mutable borrow.
1019     Borrow(Region<'tcx>),
1020     /// Used as base for another place, e.g. `x` in `x.y`. Could potentially mutate the place.
1021     /// For example, the projection `x.y` is marked as a mutation in these cases:
1022     ///
1023     ///     x.y = ...;
1024     ///     f(&mut x.y);
1025     ///
1026     Projection,
1027     /// Retagging, a "Stacked Borrows" shadow state operation
1028     Retag,
1029 }
1030
1031 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1032 pub enum NonUseContext {
1033     /// Starting a storage live range.
1034     StorageLive,
1035     /// Ending a storage live range.
1036     StorageDead,
1037     /// User type annotation assertions for NLL.
1038     AscribeUserTy,
1039 }
1040
1041 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
1042 pub enum PlaceContext<'tcx> {
1043     NonMutatingUse(NonMutatingUseContext<'tcx>),
1044     MutatingUse(MutatingUseContext<'tcx>),
1045     NonUse(NonUseContext),
1046 }
1047
1048 impl<'tcx> PlaceContext<'tcx> {
1049     /// Returns `true` if this place context represents a drop.
1050     pub fn is_drop(&self) -> bool {
1051         match *self {
1052             PlaceContext::MutatingUse(MutatingUseContext::Drop) => true,
1053             _ => false,
1054         }
1055     }
1056
1057     /// Returns `true` if this place context represents a borrow.
1058     pub fn is_borrow(&self) -> bool {
1059         match *self {
1060             PlaceContext::NonMutatingUse(NonMutatingUseContext::SharedBorrow(..)) |
1061             PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow(..)) |
1062             PlaceContext::NonMutatingUse(NonMutatingUseContext::UniqueBorrow(..)) |
1063             PlaceContext::MutatingUse(MutatingUseContext::Borrow(..)) => true,
1064             _ => false,
1065         }
1066     }
1067
1068     /// Returns `true` if this place context represents a storage live or storage dead marker.
1069     pub fn is_storage_marker(&self) -> bool {
1070         match *self {
1071             PlaceContext::NonUse(NonUseContext::StorageLive) |
1072             PlaceContext::NonUse(NonUseContext::StorageDead) => true,
1073             _ => false,
1074         }
1075     }
1076
1077     /// Returns `true` if this place context represents a storage live marker.
1078     pub fn is_storage_live_marker(&self) -> bool {
1079         match *self {
1080             PlaceContext::NonUse(NonUseContext::StorageLive) => true,
1081             _ => false,
1082         }
1083     }
1084
1085     /// Returns `true` if this place context represents a storage dead marker.
1086     pub fn is_storage_dead_marker(&self) -> bool {
1087         match *self {
1088             PlaceContext::NonUse(NonUseContext::StorageDead) => true,
1089             _ => false,
1090         }
1091     }
1092
1093     /// Returns `true` if this place context represents a use that potentially changes the value.
1094     pub fn is_mutating_use(&self) -> bool {
1095         match *self {
1096             PlaceContext::MutatingUse(..) => true,
1097             _ => false,
1098         }
1099     }
1100
1101     /// Returns `true` if this place context represents a use that does not change the value.
1102     pub fn is_nonmutating_use(&self) -> bool {
1103         match *self {
1104             PlaceContext::NonMutatingUse(..) => true,
1105             _ => false,
1106         }
1107     }
1108
1109     /// Returns `true` if this place context represents a use.
1110     pub fn is_use(&self) -> bool {
1111         match *self {
1112             PlaceContext::NonUse(..) => false,
1113             _ => true,
1114         }
1115     }
1116
1117     /// Returns `true` if this place context represents an assignment statement.
1118     pub fn is_place_assignment(&self) -> bool {
1119         match *self {
1120             PlaceContext::MutatingUse(MutatingUseContext::Store) |
1121             PlaceContext::MutatingUse(MutatingUseContext::Call) |
1122             PlaceContext::MutatingUse(MutatingUseContext::AsmOutput) => true,
1123             _ => false,
1124         }
1125     }
1126 }